CIT 383: Administrative Scripting

1. Directories CIT 383: Administrative Scripting CIT 383: Administrative Scripting

2. CIT 383: Administrative Scripting Topics • Directories • Inodes • File Management • Command Line Arguments

3. CIT 383: Administrative Scripting Directories Directory: table of name to inode mappings $ ls –i / 2272929 bin 65409 boot 49057 cdrom 2260 dev 850305 etc 2 home 2371041 initrd 49075 initrd.img 49058 initrd.img.old 948417 lib

4. CIT 383: Administrative Scripting Accessing Directories thisdir = Dir.new(pathname) absolutedir = Dir.new(‘/home/smi/dir1’) relativedir = Dir.new(‘smi/dir1’) currentdir = Dir.new(‘.’) uponedir = Dir.new(‘..’) Methods entries: returns array of filenames each: iterates over each file in directory

5. CIT 383: Administrative Scripting Inodes An inode is a disk structure that contains • Size of the file in bytes. • Device ID that identifies device where file is located. • UID of the file’s owner. • GID of the file’s group. • File mode (permissions.) • Timestamps • ctime: inode change time • mtime: time file content was last modified • atime: time file content was last accessed • Reference count that identifies how many directory entries point to inode. • Pointers to disk blocks containing file data.

6. CIT 383: Administrative Scripting Hard and Symbolic Links A hard link is • A directory entry that points to an inode. • Deleting a file with rm just removes the directory entry. • File data is not removed until all links removed. A symbolic link is • A file that contains a pathname. • Deleting the link does not affect the file. • Deleting a file with rm invalidates the symbolic link but does not remove it from filesystem.

7. Basic File Permissions Three sets of permissions: owner, group, world • Each set represented by an octal digit. • Each permission (r,w,x) one bit in octal digit. • Special permissions: setuid, setgid, sticky. ex: chmod 0644 file u: rw, g: r, o: r ex: chmod 0711 bin u: rwx, g: x, o: x CIT 383: Administrative Scripting

8. CIT 383: Administrative Scripting File::Stat The File::Stat class allows access to inodes stat = File::Stat.new(pathname) OR file = File.new(pathname) stat = file.stat Methods size: size of file in bytes uid: UID of file owner gid: GID of file owner mode: file permissions in octal mtime,ctime,atime: file timestamps

9. CIT 383: Administrative Scripting Querying File Attributes directory? – Is file a directory? symlink? – Is file a symbolic link? file? – Is file an ordinary file (not a directory, device, or symlink)? readable? – Is file readable by me? writable? – Is file writable by me? executable? – Is file executable by me? setuid? – Is file setuid? setgid? – Is file setgid? sticky? – Is the sticky bit set?

10. CIT 383: Administrative Scripting File Management The FileUtils class provides methods that emulate the functionality of UNIX commands: chmod chown cp ln mkdir mv rm rmdir

11. CIT 383: Administrative Scripting Command Line Arguments Using command line arguments ./test.rb arg1 arg2 arg3 Accessing command line arguments Ruby provides them via the ARGV array: ARGV.each do |arg| puts arg end

12. CIT 383: Administrative Scripting References • Michael Fitzgerald, Learning Ruby, O’Reilly, 2008. • David Flanagan and Yukihiro Matsumoto, The Ruby Programming Language, O’Reilly, 2008. • Hal Fulton, The Ruby Way, 2nd edition, Addison-Wesley, 2007. • Robert C. Martin, Clean Code, Prentice Hall, 2008. • Dave Thomas with Chad Fowler and Andy Hunt, Programming Ruby, 2nd edition, Pragmatic Programmers, 2005.